I actually had an entire imaginary society, Project Reality. The "project" we were trying to accomplish was to create another world to live in when we got tired of Earth (read: ASAP). We had some pretty elaborate schemes, involving portals and time travel and whatnot, in hidden areas in various wooded areas.
A few of the project's members, if I remember correctly: Annie Dinny, who was my age and my best friend; Andro Gene, whom I eventually married; Jack Dodger, the six-inch-tall elf who kept the library; and Paul McCartney. I'm not sure why he got involved. I must have been an odd child.
A childhood belief about imaginary friends

others believed things like this
- My daughter thought Paul McCartney was singing "Hey Dude" instead of "Hey Jude". Anon
- That the McCartney Era was another name for Beatlemania (due to confusion between "McCartney" and "McCarthy"— James Anderson
- I used to believe there was a secret door to the gremlin world hidden under my bed— Mel
- I used to have an imaginary friend named Mr. Nobody. He would protect me from my imaginary enemy, Bad Elmer.— Kdees
- my sister used to tell me that manhole covers were direct portals to hell.— autumn
- When i was about 3 or 4 i thought Gene Simmons was the Boogie Man.— miss13